1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member. More particularly, it relates to an electrophotographic photosensitive member comprising an intermediate layer having both functions as an adhesive layer and a barrier layer, provided between a support and a photosensitive layer.
1. Related Background Art
In general, in electrophotographic photosensitive members of a Carlson type, charge characteristics of photosensitive members, i.e., the stabilities at dark portion potential and light portion potential, are important in order to obtain a good image having a constant image density and also free of background staining in the course of the repetition of a process comprising the steps of charging, imagewise exposure, transfer, cleaning, and pre-exposure.
In photosensitive members having laminated structure in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer, the charge generation layer is commonly provided as a very thin layer of, for example, about 0.5 .mu.m thick, so that defects, stain, deposits or scratches on the surface of a support may cause non-uniformity in the film thickness of the charge generation layer. Non-uniformity of the film thickness of the charge generation layer causes uneven sensitivity in the photosensitive member, and hence it is required to make the charge generation layer as uniform as possible. It is also known that its adhesion to the support influences the characteristics of the photosensitive member.
Under such circumstances, it has been hitherto proposed that an intermediate layer having a function as a barrier layer and a function as an adhesive layer is provided between the charge generation layer and the support.
As materials to form the layer provided between the photosensitive layer and the support, it is conventionally known to use polyamides (Japanese Patent Application laid-open No. 46-47344 and No. 52-25638, polyesters (Japanese Patent Application laid-open No. 52-20836 and No. 54-26738), polyurethanes (Japanese Patent Application laid-open No. 49-10044 and No. 53-89435), casein (Japanese Patent Application laid-open No. 55-103556), polypeptides (Japanese Patent Application laid-open No. 53-48523), polyvinyl alcohols (Japanese Patent Application laid-open No. 52-100240), polyvinyl pyrrolidone (Japanese Patent Application laid-open No. 48-30936), a vinyl acetate/ethylene copolymer (Japanese Patent Application laid-open No. 48-26141), a maleic anhydride ester polymer (Japanese Patent Application laid-open No. 52-10138), polyvinyl butyral (Japanese Patent Application laid-open No. 57-90639 and No. 58-106549), quaternary ammonium salt-containing polymers (Japanese Patent Application laid-open No. 51-126149 and No. 56-60448), ethyl cellulose (Japanese Patent Application laid-open No. 55-143564), etc.
In the electrophotographic photosensitive members that use the above materials in the intermediate layer, however, the resistance of the intermediate layer may change with changes in temperature and humidity, and therefore it has been difficult to obtain potential characteristics and images that can be always stable to all environmental conditions of from the low temperature and low humidity to the high temperature and high humidity.
For example, when a photosensitive member is repeatedly used under conditions of low temperature and low humidity that increase the resistance of the intermediate layer, electric charge remains in the intermediate layer and hence the light portion potential and residual potential increase to cause fog on a copied image. When such a photosensitive member is used in a printer of an electrophotographic system in which reversal development is carried out, there have been the problems that the resulting image has a low density and no copies with constant image quality are obtainable.
Under conditions of high temperature and high humidity, the function as a barrier is lowered because the intermediate layer changes to have a low resistance, resulting in a lowering of the dark portion potential because of an increase in the injection of carriers from the support side. Thus, under conditions of the high temperature and high humidity, there have been the problems that the resulting copied image has a low density, and black-spot faulty fog tends to occur in the image when such a photosensitive member is used in the printer of an electrophotographic system in which reversal development is carried out.